The formation of the solar system

Initially the cloud was about several light years across. A small overdensity in the cloud caused the contraction to begin and the overdensity to grow, thus producing a faster contraction –> run away or collapse process

Initially, most of the motions of the cloud particles were random, yet the nebula had anet rotation. As collapse proceeded, the rotation speed of the cloud was gradually increasing due to conservation of angular momentum.

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Gravitational collapse was much more efficient along the spin axis, so the rotating ball collapsed into thin disk with a diameter of 200 AU (0.003 light years) (twice Pluto’s orbit), aka solar nebula (movie), with most of the mass concentrated near the center.

As the cloud contracted, its gravitational potential energy was converted into kinetic energy of the individual gas particles. Collisions between particles converted this energy into heat (random motions). The solar nebula became hottest near the center where much of the mass was collected to form the protosun(the cloud of gas that became Sun).
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